OBJECTIVES: I. Determine the response in patients with androgen-independent prostate cancer treated with calcitriol and carboplatin. II. Determine the palliative response in patients with cancer-related pain treated with this regimen. III. Determine the response in patients with bidimensionally measurable disease treated with this regimen. IV. Determine the duration of prostate-specific antigen, palliative, and measurable disease responses in patients treated with this regimen. V. Determine the survival of patients treated with this regimen. VI. Assess the quality of life of patients treated with this regimen. VII. Determine the qualitative and quantitative toxic effects of this regimen in these patients.